Graphene, composition for preparing graphene, and method of preparing graphene using the composition

ABSTRACT

Graphene, a composition for preparing graphene, and a method of preparing graphene using the composition are disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Rule 53(b) Divisional Application of U.S.application Ser. No. 14/655,461 filed Jun. 25, 2015, which is a NationalStage of International Application No. PCT/KR2013/012058 filed Dec. 24,2013, which claims the benefit of Korean Patent Application No.10-2012-0153705, filed on Dec. 26, 2012, in the Korean IntellectualProperty Office, the contents of all of which are incorporated herein byreference in their entirety.

BACKGROUND 1. Field

One or more exemplary embodiments relate to graphene, a composition forpreparing graphene, and a method of preparing graphene using thecomposition.

2. Description of the Related Art

Developments of new materials are actively being progressed in variouselectronic device fields such as display devices and solar cells.Particularly, studies are being actively progressed on new materialsthat are capable of replacing indium tin oxides (ITOs) mainly used as atransparent electrode of an electronic device. Studies are beingintensively made on carbon-containing materials among the new materials,e.g., carbon nanotubes, diamond, graphite, graphene, or the like.

Particularly, since graphene is excellent in terms of electricconductivity and transparency, various methods of preparing graphenehave been suggested. The methods of preparing graphene may largely bedivided into mechanical methods and chemical methods for preparinggraphene. The mechanical methods of preparing graphene may includemethods of detaching graphene from a graphite sample using a scotchtape. Such methods using a scotch tape may prevent damage of a surfaceof graphene, but are not suitable for upsizing graphene. The CVD methodis a method of injecting a vapor phased carbon supply source into acontainer in which a metal catalyst is disposed, heating the container,and then cooling the heated container again to grow a graphene sheet onthe surface of the metal catalyst. The CVD method may also involve astep of removing the metal catalyst. Methods typically used for removingthe metal catalyst (e.g., etching with a salt solution) in the relatedart may damage the surface of graphene, and thus a graphene sheet havinga low sheet resistance value may not be easily formed.

SUMMARY

One or more exemplary embodiments include graphene having a low sheetresistance value, a composition for preparing graphene, and a method ofpreparing graphene using the composition.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to one or more exemplary embodiments, graphene includes anitrogen-containing organic compound.

According to one or more exemplary embodiments, a composition forpreparing graphene includes a nitrogen-containing organic compound; anoxidizing agent; and an acid.

According to one or more exemplary embodiments, a method of preparinggraphene includes doping graphene with a composition for preparinggraphene to obtain a doped graphene, the composition including anitrogen-containing organic compound, an oxidizing agent, and an acid.

According to one or more exemplary embodiments, a method of preparinggraphene includes: forming graphene on at least one side of a metalcatalyst; and removing the metal catalyst and doping the graphene at thesame time with a composition for preparing graphene to obtain a dopedgraphene, the composition including a nitrogen-containing organiccompound, an oxidizing agent, and an acid.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a diagram schematically illustrating a method of preparinggraphene according to an exemplary embodiment of the present inventiveconcept;

FIG. 2 is a diagram schematically illustrating a method of preparinggraphene according to another exemplary embodiment of the presentinventive concept;

FIG. 3 is a diagram schematically illustrating a method of preparinggraphene according to another exemplary embodiment of the presentinventive concept; and

FIG. 4 is a diagram schematically illustrating a method of preparinggraphene according to another exemplary embodiment of the presentinventive concept.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theexemplary embodiments are merely described below, by referring to thefigures, to explain aspects of the present description. As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items. Expressions such as “at least one of,” whenpreceding a list of elements, modify the entire list of elements and donot modify the individual elements of the list.

Hereinafter, graphene, a composition for preparing graphene, and amethod of preparing graphene using the composition according to anexemplary embodiment of the present inventive concept are described morein detail.

The term “graphene” used in the present specification refers to multiplecarbon atoms connected to one another by a covalent bond such that thecarbon atoms are formed in a two-dimensional film form (normally sp²bond). The carbon atoms composing graphene form a 6-membered ring as abasic repeating unit, but may additionally include a 5-membered ringand/or a 7-membered ring. According to amount(s) of the 5-membered ringand/or the 7-membered ring that may be contained in graphene, the formof graphene may be varied. Graphene may be formed in a single layer, butmultiple single layers may be laminated to form a multi-layer. Here, thelayer of graphene may have a maximum thickness of about 100 nm.

The term “a composition for preparing graphene” used in the presentspecification refers to a composition that removes a metal catalyst usedin the preparation of graphene and/or that is used in doping graphene.

The term “a laminate” used in the present specification refers to aplurality of layers, i.e., a state of additionally including one or moreof a metal catalyst, a carrier film, and a target film besides graphenedepending on the respective steps of a method of preparing grapheneaccording to an exemplary embodiment of the present inventive concept.

According to an aspect of the present inventive concept, graphene mayinclude a nitrogen-containing organic compound. The nitrogen-containingorganic compound is a carbon compound containing a nitrogen atom, andtypes of the nitrogen-containing organic compound is not particularlylimited so long as a sheet resistance value of graphene may be lowered.The nitrogen-containing organic compound may be chemically and/orphysically bonded to the surface of graphene, and may be chemicallyand/or physically bonded between multiple layers composing graphene, butthe nitrogen-containing organic compound is not limited thereto. Thatis, if a sheet resistance value of graphene may be lowered, bondingpositions or bonding methods of the nitrogen-containing organic compoundare not limited.

In the case of doping graphene using a metal salt such as AuCl₃, a sheetresistance value of graphene may be lowered while transmittance ofgraphene may be lowered. Meanwhile, in the case of doping graphene usingan acid such as HNO₃, a sheet resistance value of graphene may belowered while transmittance of graphene may also be maintained. However,such doping effects may not be lasted for a long time.

However, in the case of doping graphene using the nitrogen-containingorganic compound, a sheet resistance value of graphene may be loweredwhile transmittance of graphene may be maintained. In addition, thelowered sheet resistance value of graphene may be maintained for a longtime.

For example, the nitrogen-containing organic compound may be at leastone substituted or unsubstituted C₂-C₆₀ heteroaryl group, but is notlimited thereto.

For example, the nitrogen-containing organic compound may be at leastone selected from a substituted or unsubstituted pyrrole, a substitutedor unsubstituted imidazole, a substituted or unsubstituted pyrazole, asubstituted or unsubstituted pyridine, a substituted or unsubstitutedpyrazine, a substituted or unsubstituted pyrimidine, a substituted orunsubstituted pyridazine, a substituted or unsubstituted indole, asubstituted or unsubstituted quinoline, a substituted or unsubstitutedbenzoquinoline, a substituted or unsubstituted benzimidazole, asubstituted or unsubstituted triazine, and a substituted orunsubstituted carbazole, but the nitrogen-containing organic compound isnot limited thereto.

For example, the nitrogen-containing organic compound may be at leastone selected from a pyrrole, an imidazole, a pyrazole, a pyridine, apyrazine, a pyrimidine, a pyridazine, an indole, a quinoline, abenzoquinoline, a benzimidazole, a triazine, and a carbazole; and apyrrole, an imidazole, a pyrazole, a pyridine, a pyrazine, a pyrimidine,a pyridazine, an indole, a quinoline, a benzoquinoline, a benzimidazole,a triazine, and a carbazole, each substituted with at least one of adeuterium, a halogen atom, a methyl group, an ethyl group, an n-propylgroup, an i-propyl group, an n-butyl group, an i-butyl group, and at-butyl group, but the nitrogen-containing organic compound is notlimited thereto.

For example, the nitrogen-containing organic compound may be at leastone selected from an imidazole and a benzimidazole; and an imidazole anda benzimidazole, each substituted with at least one of a deuterium, amethyl group, and an ethyl group, but the nitrogen-containing organiccompound is not limited thereto.

For example, the nitrogen-containing organic compound may be at leastone selected from an imidazole, a benzimidazole, a5,6-dimethylbenzimidazole, and a 1,2-dimethylbenzimidazole, but thenitrogen-containing organic compound is not limited thereto.

The graphene doped with the nitrogen-containing organic compound mayhave a sheet resistance value of about more than 0 Ω/sq to about 300Ω/sq or less, e.g., about 100 Ω/sq to about 200 Ω/sq.

In an exemplary embodiment, the graphene doped with thenitrogen-containing organic compound may be used to replace an existingITO electrode, but graphene is not limited thereto. Specifically, thegraphene may be used as a transparent electrode, and more specifically,the graphene may be used as a transparent electrode for touch panels. Inaddition, the graphene may be used as an electrode for a solar cell.

According to another aspect of the present inventive concept, acomposition for preparing graphene may include a nitrogen-containingorganic compound; an oxidizing agent; and an acid. When a compositionincluding both a nitrogen-containing organic compound and an acid isused for the preparation of graphene, a sheet resistance value ofgraphene may be lowered. For example, when a composition including anitrogen-containing organic compound but not including an acid is usedfor the preparation of graphene, a sheet resistance value of graphenemay not be lowered. That is, a composition including only anitrogen-containing organic compound is used for the preparation ofgraphene, graphene may not be doped.

The nitrogen-containing organic compound may have a function to lower asheet resistance value of graphene. The nitrogen-containing organiccompound may be at least one selected from a substituted orunsubstituted C₂-C₆₀ heteroaryl group, but the nitrogen-containingorganic compound is not limited thereto.

For example, the nitrogen-containing organic compound may be at leastone selected from a substituted or unsubstituted pyrrole, a substitutedor unsubstituted imidazole, a substituted or unsubstituted pyrazole, asubstituted or unsubstituted pyridine, a substituted or unsubstitutedpyrazine, a substituted or unsubstituted pyrimidine, a substituted orunsubstituted pyridazine, a substituted or unsubstituted indole, asubstituted or unsubstituted quinoline, a substituted or unsubstitutedbenzoquinoline, a substituted or unsubstituted benzimidazole, asubstituted or unsubstituted triazine, and a substituted orunsubstituted carbazole, but the nitrogen-containing organic compound isnot limited thereto. For example, the nitrogen-containing organiccompound may be at least one selected from: a pyrrole, an imidazole, apyrazole, a pyridine, a pyrazine, a pyrimidine, a pyridazine, an indole,a quinoline, a benzoquinoline, a benzimidazole, a triazine, and acarbazole; and a pyrrole, an imidazole, a pyrazole, a pyridine, apyrazine, a pyrimidine, a pyridazine, an indole, a quinoline, abenzoquinoline, a benzimidazole, a triazine, and a carbazole, eachsubstituted with at least one of a deuterium, a halogen atom, a methylgroup, an ethyl group, an n-propyl group, an i-propyl group, an n-butylgroup, an i-butyl group, and a t-butyl group, but thenitrogen-containing organic compound is not limited thereto.

For example, the nitrogen-containing organic compound may be at leastone selected from: an imidazole and a benzimidazole; and an imidazoleand a benzimidazole, each substituted with at least one of a deuterium,a methyl group, and an ethyl group, but the nitrogen-containing organiccompound is not limited thereto.

For example, the nitrogen-containing organic compound may be at leastone selected from an imidazole, a benzimidazole, a5,6-dimethylbenzimidazole, and a 1,2-dimethylbenzimidazole, but thenitrogen-containing organic compound is not limited thereto.

The oxidizing agent may be at least one selected from H₂O₂, (NH₄)S₂O₈,HClO, and ClO₄, but the oxidizing agent is not limited thereto. Forexample, the oxidizing agent may be H₂O₂. In addition, the oxidizingagent may be introduced in a solid form into the composition forpreparing graphene, or the oxidizing agent may be introduced in a statethat the oxidizing agent is diluted into a solvent such as water.

The acid may be at least one selected from H₂SO₄, HNO₃, H₃PO₄, HCl, andCH₃COOH, but the acid is not limited thereto. The acid may be introducedinto the composition for preparing graphene in a state that the acid isdiluted into a solvent such as water. For example, the acid may be a 95wt % aqueous sulfuric acid solution or an 85 wt % aqueous phosphoricacid solution.

The composition for preparing graphene may include about 0.2 wt % toabout 10 wt % of the nitrogen-containing organic compound, about 1 wt %to about 10 wt % of the oxidizing agent, about 2 wt % to about 30 wt %of the acid, and a balance of a solvent. However, the composition forpreparing graphene composition for preparing graphene is not limitedthereto. In the present specification, contents of thenitrogen-containing organic compound, the oxidizing agent, and the acidare based on total weights of the composition for preparing graphene.The composition for preparing graphene may include, for example, about0.5 wt % or more, about 1 wt % or more, about 2.5 wt % or less, or about2 wt % or less of the nitrogen-containing organic compound. Thecomposition for preparing graphene may include, for example, about 2 wt% or more, about 3 wt % or more, about 9 wt % or less, or about 8 wt %or less of the oxidizing agent. The composition for preparing graphenemay include, for example, about 3 wt % or more, about 5 wt % or more,about 18 wt % or less, or about 15 wt % or less of the acid.

Water may be used as a solvent of the composition for preparinggraphene. That is, the composition for preparing graphene may be anaqueous solution of a nitrogen-containing organic compound, an oxidizingagent, and an acid. However, materials are not particularly limited ifthe solvent includes any materials that are capable of homogeneouslydispersing the oxidizing agent and acid. Therefore, besides water, thesolvent may additionally include other liquids that are compatible withwater. Alternatively, the solvent may additionally include an organicsolvent such as tetrahydrofuran to disperse the nitrogen-containingorganic compound homogeneously.

The composition for preparing graphene may additionally includeadditives, and any additives widely known in the art may be used in thepresent inventive concept. For example, the additives include adispersant, a storage stabilizer, a stabilizer, and mixtures thereof.The additives may be contained in amount ranges of about 3 wt % to about20 wt % based on the total weight of the composition for preparinggraphene.

The nitrogen-containing organic compound, the oxidizing agent, the acid,and the solvent are mixed in-situ such that the mixture may be used asthe composition for preparing graphene. Alternatively, after mixing thenitrogen-containing organic compound, the oxidizing agent, the acid, andthe solvent to prepare a composition, the prepared composition may bestored and used. Particularly, when the prepared composition is storedand used after mixing the nitrogen-containing organic compound, theoxidizing agent, the acid, and the solvent to prepare a composition, thecomposition for preparing graphene may additionally include additivessuch as a dispersant, a storage stabilizer, or the like. In addition,when the composition for preparing graphene includes H₂O₂ as theoxidizing agent, the composition for preparing graphene may additionallyinclude additives such as a stabilizer for controlling the oxidationreaction of H₂O₂.

FIG. 1 is a diagram schematically illustrating a method of preparinggraphene according to an exemplary embodiment. Hereinafter, a method ofpreparing graphene is described as follows by referring to FIG. 1.

A carrier film 120 is combined with one side of graphene 110.

Any types of the carrier film 120 may be used if the carrier film 120supports the graphene 110 to facilitate transfer of the graphene 110,maintains the shape of the graphene 110, and prevents damages of thegraphene 110. For example, the carrier film 120 may be a thermal releasetape or a polymer support, but the carrier film 120 is not limitedthereto. Although one side of the thermal release tape has adhesiveproperty at room temperature, the thermal release tape has properties ofloosing adhesive property at a predetermined temperature or higher. Thepolymer support includes polymers such as polymethylmethacrylate (PMMA),and the polymer may be removed by an organic solvent at a desired timeafter forming a polymer on one side of the graphene 110 by a solutionprocess.

A laminate of the graphene 110 and the carrier film 120 is doped with acomposition for preparing graphene including the nitrogen-containingorganic compound, the oxidizing agent, and the acid, to obtain dopedgraphene 130.

Functions, types, using forms, or contents of the nitrogen-containingorganic compound, the oxidizing agent, and the acid are referred to theabove-mentioned composition for preparing graphene.

Any steps of obtaining the doped graphene 130 may be used if the stepsare capable of obtaining doped graphene. For example, the step may beperformed by impregnating the laminate of the graphene 110 and thecarrier film 120 with the composition for preparing graphene or byspraying the composition for preparing graphene onto the laminate of thegraphene 110 and the carrier film 120.

The doped graphene 130 is transferred onto a target film 140.

The target film 140 may be a portion of a device to which the dopedgraphene 130 is applied, and specifically may be one surface of anelectrode of the device.

To transfer the doped graphene 130 onto the target film 140, thelaminate of the graphene 110 and the carrier film 120 is combined withthe target film 140, and then, the carrier film 120 is removed. Forexample, when the carrier film 120 is a thermal release tape, thethermal release tape is detached from the doped graphene 130 by applyinga force to the doped graphene 130 at a predetermined temperature orhigher at which the thermal release tape looses adhesive property. Forexample, when the carrier film 120 is a polymer support, an organicsolvent such as acetone is applied to the polymer support to remove thepolymer support from the doped graphene 130.

FIG. 2 is a diagram schematically illustrating a method of preparinggraphene according to another exemplary embodiment. Hereinafter, amethod of preparing graphene is described as follows by referring toFIG. 2.

A target film 240 is combined with one side of graphene 210.

A description of the target film 240 is referred to the description ofthe target film 140 of FIG. 1.

A laminate of the graphene 210 and the target film 240 is doped with acomposition for preparing graphene including the nitrogen-containingorganic compound, the oxidizing agent, and the acid, to obtain dopedgraphene 230.

Functions, types, using forms, contents, etc of the nitrogen-containingorganic compound, the oxidizing agent, and the acid are referred to theabove-mentioned composition for preparing graphene.

A description on the step of obtaining the doped graphene 230 isreferred to the description on the step of obtaining the doped graphene130 of FIG. 1.

FIG. 3 is a diagram schematically illustrating a method of preparinggraphene according to another exemplary embodiment. Hereinafter, amethod of preparing graphene is described as follows by referring toFIG. 3.

Although it is not illustrated in the drawing, a metal catalyst 350 ispretreated.

The metal catalyst 350 may be used as a place at which graphene isgrown. Forms of the metal catalyst 350 are not limited if the grapheneis grown at the metal catalyst 350. For example, the metal catalyst 350may be a sheet, a substrate, or a film.

The metal catalyst 350 may be at least one selected from copper (Cu),nickel (Ni), cobalt (Co), iron (Fe), platinum (Pt), gold (Au), silver(Ag), aluminum (Al), chromium (Cr), magnesium (Mg), manganese (Mn),molybdenum (Mo), rhodium (Rh), silicon (Si), tantalum (Ta), titanium(Ti), tungsten (W), uranium (U), vanadium (V), palladium (Pd), yttrium(Y), zirconium (Zr), germanium (Ge) and alloys thereof, but the metalcatalyst 350 is not limited thereto.

The metal catalyst 350 may be a single layer, or may be an outermostlayer of a multilayer substrate consisting of two or more layers.

A hydrogen gas may be used in a process of pretreating the metalcatalyst 350 to remove foreign materials present on the surface of themetal catalyst 350. In addition, the process of pretreating the metalcatalyst 350 may reduce defects of graphene during the formation ofgraphene by cleaning the surface of the metal catalyst 350 by using anacid, an alkali solution, or the like. The process of cleaning thesurface of the metal catalyst 350 may be omitted as occasion demands.

Graphene 310 is formed on at least one side of the metal catalyst 350.

Steps of forming the graphene 310 on the at least one side of the metalcatalyst 350 are not limited to particular methods. For example, variousprocesses such as chemical vapor deposition (CVD), thermal chemicalvapor deposition (TCVD), rapid thermal chemical vapor deposition(RTCVD), inductive coupled plasma chemical vapor deposition (ICP-CVD),and atomic layer deposition (ATLD) may be used in the step. Non-limitingexamples of the step may include CVD.

CVD is a method of growing a graphene sheet on the surface of the metalcatalyst by cooling the heated container again after injecting a vaporphased carbon supply source into a container in which a metal catalystis disposed and heating the container.

The vapor phased carbon supply source may be carbon monoxide, ethane,ethylene, ethanol, acetylene, propane, butane, butadiene, pentane,pentene, cyclopentadien, hexane, cyclohexane, benzene, toluene, ormixtures of two or more thereof. Such a vapor phased carbon supplysource is separated into carbon atoms and hydrogen atoms at a hightemperature. The separated carbon atoms are deposited onto the heatedmetal catalyst 350, and a graphene 310 is formed while the metalcatalyst 350 is being cooled.

The graphene 310 may be formed on at least side of the metal catalyst350. As shown in FIG. 3, the graphene 310 may be formed on one side ofthe metal catalyst 350, but the formation of the graphene 310 is notlimited thereto. The graphene 310 may also be formed on both sides ofthe metal catalyst 350.

A carrier film 320 is formed on one side of the graphene 310 on which isthe metal catalyst 350 is formed.

A description on the carrier film 320 is referred to the description onthe carrier film 120 of FIG. 1.

A doped graphene 330 is obtained by applying a composition for preparinggraphene including the nitrogen-containing organic compound, theoxidizing agent and the acid to a laminate of a carrier film 320, agraphene 310 and a metal catalyst 350, thereby removing the metalcatalyst 350 and doping the graphene 310 at the same time.

Since the metal catalyst 350 is removed and the graphene 330 is doped atthe same time, the doped graphene 330 may be economically prepared. Thatis, a cost for preparing the doped graphene is reduced since the methodmay omit a preparation process of one step compared to a method ofremoving the metal catalyst and then doping the graphene. In addition, alowered sheet resistance value of the doped graphene 330 may bemaintained for a long time by using the composition for preparinggraphene.

The step of simultaneously removing the metal catalyst 350 and dopingthe graphene 310 to obtain the doped graphene 330 may be performed forabout 3 minutes to about 60 minutes. For example, the composition forpreparing graphene may simultaneously remove the metal catalyst 350 anddope the graphene 310 within a time range of about 3 minutes to about 60minutes, e.g., about 3 minutes to about 15 minutes, or about 5 minutesto about 10 minutes. Since the graphene 310 may be sufficiently dopedwhile the metal catalyst 350 is substantially completely removed whenapplying a time range of about 3 minutes to about 60 minutes, a sheetresistance value of the doped graphene 330 obtained may be lowered tothe maximum. A time range of using the composition for preparinggraphene may be appropriately controlled according to circumstances.

The composition for preparing graphene may be used in an amount of about500 mL to about 1,000 mL per about 50 g of the metal catalyst 350.

The doped graphene 330 is transferred onto a target film 340.

To transfer the doped graphene 330 onto the target film 340, a method ofcombining a laminate of the graphene 310 and the carrier film 320 withthe target film 340 is referred to the description of FIG. 1.

A description on the target film 340 is referred to the target film 140of FIG. 1.

FIG. 4 is a diagram schematically illustrating a method of preparinggraphene according to another exemplary embodiment. Hereinafter, amethod of preparing graphene is described as follows by referring toFIG. 4.

Although it is not illustrated in the drawing, a metal catalyst 450 ispretreated.

A description on the step of pretreating the metal catalyst 450 isreferred to the description on the step of pretreating the metalcatalyst 350 of FIG. 3.

A graphene 410 is formed on at least one side of the metal catalyst 450.

A description on the step of forming the graphene 410 on the at leastone side of the metal catalyst 450 is referred to the description on thestep of forming the graphene 310 on the at least one side of the metalcatalyst 350 of FIG. 3.

The graphene 410 may be formed on at least side of the metal catalyst450. As shown in FIG. 4, the graphene 410 may be formed on both sides ofthe metal catalyst 450, but the formation of the graphene 410 is notlimited thereto. The graphene 410 may also be formed on one side of themetal catalyst 450.

A carrier film 420 is combined with one side of the graphene 410 onwhich the metal catalyst 450 is formed.

A description on the carrier film 420 is referred to the description onthe carrier film 120 of FIG. 1.

The metal catalyst 450 is removed.

The step of removing the metal catalyst 450 is not limited to aparticular method. For example, the step of removing the metal catalyst450 may be performed by an electrochemical separation method.

The electrochemical separation method is a method of separating thegraphene from the metal catalyst by immersing a laminate of a metalcatalyst and a graphene into an electrolyte solution and applying avoltage to the laminate. The electrochemical separation method is usedto separate a graphene formed on both sides of the metal catalyst suchthat all of the separated graphene may be used.

The electrolyte solution may include at least one selected from NaOH,Na₂CO₃, Na₃PO₄, Na₂SiO₃, and sodium silicate, but the electrolytesolution is not limited thereto.

The voltage may be about 3 V to about 30 V, the voltage is not limitedthereto.

A composition for preparing graphene including a nitrogen-containingorganic compound, an oxidizing agent, and an acid is applied to alaminate of the carrier film 420 and the graphene 410, and the graphene410 is doped with the composition for preparing graphene to obtain adoped graphene 430.

The composition for preparing graphene is used such that a lowered sheetresistance value of the doped graphene 430 may be maintained for a longtime.

A description on the step of doping the graphene 410 to obtain the dopedgraphene 430 is referred to the description on the step of doping thegraphene 110 to obtain the doped graphene 130 of FIG. 1.

The doped graphene 430 is transferred onto a target film 440.

To transfer the doped graphene 430 onto the target film 440, a method ofcombining the laminate of the graphene 410 and the carrier film 420 withthe target film 440 is referred to the description of FIG. 1.

A description on the target film 440 is referred to the target film 140of FIG. 1.

Hereinbefore, the method of preparing graphene is described by referringto FIGS. 1 to 4, but is not limited thereto.

Hereinafter, one or more embodiments will be described in more detailwith reference to the following examples. However, these examples arefor illustrative purposes only and are not intended to limit the scopeof the one or more embodiments.

EXAMPLE 1

A 35 μm copper (Cu) plate was charged into a CVD furnace. After flowingCH₄ into the furnace in a flow rate of about 30 standard cubiccentimeters per minute (sccm) at a temperature of about 1,000° C. forabout 5 minutes, the Cu plate was cooled to a temperature of about 600°C. in a cooling rate of about 60° C./min, and then, cooled to about roomtemperature in a cooling rate of about 40° C./min in a H₂ atmosphere,thereby forming graphene on Cu.

A laminate of Cu and graphene was immersed into an aqueous 4 wt %(NH₄)S₂O₈ solution for about 120 minutes, thereby removing Cu andobtaining graphene.

The graphene obtained therefrom was immersed into a compositionincluding 9 wt % of imidazole, 3 wt % of H₂O₂, 9 wt % of H₂SO₄, and abalance of water for about 60 minutes, thereby obtaining doped graphene.

EXAMPLE 2

A 35 μm Cu plate was charged into a CVD furnace. After flowing CH₄ intothe furnace in a flow rate of about 30 sccm at a temperature of about1,000° C. for about 5 minutes, the Cu plate was cooled to a temperatureof about 600° C. in a cooling rate of about 60° C./min, and then, cooledto about room temperature in a cooling rate of about 40° C./min in a H₂atmosphere, thereby forming graphene on Cu.

The graphene was immersed into a composition including about 9 wt % ofimidazole, 3 wt % of H₂O₂, 9 wt % of H₂SO₄, and a balance of water forabout 15 minutes, thereby removing Cu and doping obtaining the grapheneat the same time, and then, obtaining doped graphene.

COMPARATIVE EXAMPLE

A 35 μm Cu plate was charged into a CVD furnace. After flowing CH₄ intothe furnace in a flow rate of about 30 sccm at a temperature of about1,000° C. for about 5 minutes, the Cu plate was cooled to a temperatureof about 600° C. in a cooling rate of about 60° C./min, and then, cooledto about room temperature in a cooling rate of about 40° C./min in a H₂atmosphere, thereby forming graphene on Cu.

A laminate of Cu and graphene was immersed into an aqueous 4 wt %(NH₄)S₂O₈ solution for about 120 minutes, thereby removing Cu andobtaining graphene.

The graphene obtained therefrom was vapor-doped with about 70 wt % ofHNO₃ for about 3 minutes, thereby obtaining doped graphene.

EVALUATION EXAMPLE

The graphenes prepared in Examples 1 and 2 and Comparative Example weresubjected to measure sheet resistance values and changes in the sheetresistance values over time.

The sheet resistance values are average values for sheet resistancevalues measured at about 143 measuring points that are automaticallyselected by using an automatic sheet resistance meter (available fromDasol ENG). The measured results are shown in Tables 1 and 2 below.

TABLE 1 Comparative Example 1 Example 2 Example Sheet resistance 280 240400 value* (Ω/sq) *Note that the sheet resistance values above weremeasured in 48 hours after doping the graphene

TABLE 2 One day Two days Three days Four days Five days Before Afterafter after after after after doping doping doping doping doping dopingdoping Example 1 510 275 283 281 271 287 277 (Ω/sq) Example 2 —** 245242 251 247 238 240 (Ω/sq) Comparative 512 289 409 460 479 488 493Example (Ω/sq) **Note that due to simultaneous occurrence of the removalof the metal catalyst and the doping of the graphene in Example 2, asheet resistance value measured before doping the graphene was notseparately measured.

Referring to Table 1, it was confirmed that sheet resistance values ofthe graphenes could be lowered by using a composition including anitrogen-containing organic compound represented, an oxidizing agent,and an acid, thereby doping graphenes with the nitrogen-containingorganic compound. In addition, it was confirmed that the sheetresistance values of the graphenes can also be lowered by removing themetal catalyst and doping the graphenes at the same time.

Referring to Table 2, it was confirmed that the lowered sheet resistancevalues of the graphenes could be maintained for a long time positionincluding a nitrogen-containing organic compound, an oxidizing agent,and an acid.

As described above, according to the one or more of the above exemplaryembodiments, graphene having a low sheet resistance value and a longholding time of the low sheet resistance value may be provided.

It should be understood that exemplary embodiments described hereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each exemplaryembodiment should typically be considered as available for other similarfeatures or aspects in other exemplary embodiments.

While one or more exemplary embodiments have been described withreference to the figures, it will be understood by those of ordinaryskill in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the inventiveconcept as defined by the following claims.

What is claimed is:
 1. A composition for preparing graphene comprising:a nitrogen-containing organic compound; an oxidizing agent; and an acid,wherein the nitrogen-containing organic compound is at least oneselected from: an imidazole and a benzimidazole; and an imidazole and abenzimidazole, each substituted with at least one of a deuterium, amethyl group, and an ethyl group.
 2. The composition of claim 1, whereinthe oxidizing agent is at least one selected from H₂O₂, (NH₄)S₂O₈, HClO,and HClO₄.
 3. The composition of claim 1, wherein the acid is at leastone selected from H₂SO₄, HNO₃, H₃PO₄, HCl, and CH₃COOH.
 4. Thecomposition of claim 1, comprising 0.2 wt % to 10 wt % of thenitrogen-containing organic compound, 1 wt % to 10 wt % of the oxidizingagent, 2 wt % to 30 wt % of the acid, and a balance of a solvent.
 5. Amethod of preparing graphene, the method comprising: doping graphenewith a composition for preparing graphene of claim 1 to obtain dopedgraphene, the composition for preparing graphene comprising a nitrogencontaining organic compound, an oxidizing agent, and an acid.
 6. Themethod of claim 5, comprising the steps of: (a) combining a carrier filmwith one side of graphene; (b) doping a laminate of the graphene and thecarrier film with a composition for preparing graphene to obtain dopedgraphene, the composition for preparing graphene comprising anitrogen-containing organic compound, an oxidizing agent, and an acid;and (c) transferring the doped graphene onto a target film.
 7. Themethod of claim 5, comprising: combining a target film with one side ofthe graphene, followed by doping a laminate of the graphene and thetarget film with the composition for preparing graphene to obtain dopedgraphene.